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Numbers n such that 6n - 5 is not prime.
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%I #16 May 17 2016 11:57:30

%S 1,5,9,10,15,16,20,21,23,25,29,30,32,35,37,40,42,43,44,45,49,50,51,54,

%T 55,58,60,61,65,66,68,70,72,75,76,79,80,81,83,85,86,87,89,90,93,94,95,

%U 98,99

%N Numbers n such that 6n - 5 is not prime.

%F a(n) ~ n. - _Charles R Greathouse IV_, May 09 2016

%e a(2) = 5 because 6 * 5 - 5 = 25 that is composite.

%t Select[Range[100], Not[PrimeQ[6# - 5]] &] (* _Alonso del Arte_, May 09 2016 *)

%o (PARI) is(n)=!isprime(6*n-5) \\ _Charles R Greathouse IV_, May 09 2016

%K nonn,easy

%O 1,2

%A _Carlos Valencia Alonso_, May 09 2016